The food, beverage, and biopharmaceutical industries, which can be collectively referred to as the sanitary industry, have special needs in the design of the liquid piping systems in manufacturing facilities, and in particular of automatic liquid flow and pressure control valves. The safety and purity of these sanitary products require that the liquid products be free from spoilage or contamination by outside agents, including cleaning solvents or solutions used during the system cleanout, and control fluids used during the manufacturing process. In the sanitary industry, the cleanability of a valve in a liquid piping system represents an important feature. Cleanability relates to the ability to thoroughly and effectively clean a valve in-place (i.e., without being physically removed from the piping system, also referred to as “CIP”) with appropriate cleaning solvents or solutions, without leaving any residue or portion of the cleaning solvent, solution, or other liquid, such as water, used to rinse away the cleaning agents. Cleanable valves in the sanitary industry generally require that the cleaned valve be free of all residues and any portion of the cleaning or rinsing agents. The design of cleanable valves generally conforms to the following guidelines.
1. The valve body and fluid-contacting surfaces are made from solid materials and elastomers which resists corrosion from process fluids and cleaning chemicals, are typically, but not limited to, 316L stainless steel, 304 stainless steel, PVDF, TEFLON, EPDM, and Buna-N.
2. The valve body and fluid-contacting surfaces are made with smooth product contacting surfaces.
3. The valve body and fluid-contacting surfaces are made free from crevices or threads.
4. The valve body and fluid-contacting surfaces are made free from dead-legs or pockets.
5. The valve body and fluid-contacting surfaces are made completely drainable in the product-contacting area.
6. The valve body and fluid-contacting surfaces are made free from sharp corners, particularly inside corners, where product could accumulate.
7. The valve body and fluid-contacting surfaces are made with the ability to stroke the valve stem back and forth during clean-out in order to clean any dynamic O-rings, T-seals, or other sealing means, of residual product or cleaning agent which can later enter or leave the product contact areas during normal production.
These guidelines can be referred to as 3A guidelines 64-00(08-17N) for sanitary pressure regulators.
To a lesser extent, cleanable valve design also addresses the need to disassemble (e.g., by hand) the valve for hand cleaning of the product contacting areas without tools. Since most liquid flow valves are designed to be cleaned in-place using some form of automation, this guideline is sometimes relaxed. Cleanability is therefore an important distinction between a sanitary valve and a valve used in other industries.
Another important design criterion for a sanitary flow valve is the flow rate control or pressure control performance. The chemical processing operations used in the manufacture of most sanitary products are quite varied, and include filtrations, distillations, chemical reactions, separations, and others. The liquid components in such operations often require precise control of either one or more of the liquid properties, such as pressure, temperature, and flow rate. Consequently, there is an ongoing need in the sanitary industry for improved liquid flow control and fluid pressure control valves for the control of the liquid properties in the manufacture of sanitary products
A liquid pressure building regulator valve of the prior art (FIG. 1 of U.S. Pat. No. 4,208,031) is shown in FIG. 10. Numerals shown in parentheses are those of the prior art valve of FIG. 10. The liquid pressure building regulator is connected into the piping of a typical process system to control the upstream liquid pressure at a selected setpoint, P′up. A control fluid regulator (not shown) introduced via port (17) is set to maintain a controlling pressure, Pcontrol, within the actuator space above the control diaphragm 6. Product liquid flows into inlet port (18), through the orifice, and out of port (19) at a downstream pressure Pdown. When the upstream product pressure Pup is at the desired set pressure, the regulator can operate at a steady state: that is, a state at which the valve plug (20) remains stationary at a position whereat a generally constant flow of liquid flows through the orifice, at a constant pressure differential across the orifice.
FIG. 11A shows a simplified cross-sectional view of a liquid pressure building regulator of the prior art of a valve plug and orifice. FIG. 11B is a chart of the liquid pressure of the product as it passes through the orifice of the regulator. Neither figure is drawn to scale. The figures show first that there is a significant total pressure drop between the inlet at position A having a pressure (P1) and the outlet at position D having a pressure (P3), and that the minimum pressure P2 at position B within the valve occurs within the valve orifice (between the valve plug and the seat). FIG. 11B shows that there is also a slight recovery in pressure from pressure P2 at position B to the downstream pressure P3 at position D. The pressure recovery is attributed to the significant turbulence within and just downstream of the valve orifice, where kinetic energy (liquid velocity) and potential energy (liquid pressure) are in transition. For the purpose of this invention, it can be assumed that the pressure P3′ at position C pushing upward against the downstream-side of the valve plug is equal to the downstream pressure P3.
In the regulator valve of the prior art shown in FIG. 10, the effective liquid-side area of the diaphragm assembly (ALS) that is exposed to upstream liquid pressure is equal to the area of the product diaphragm (5) minus the area of the valve plug (20) where D5 is the diameter of the diaphragm (5) and D20 is the diameter of the valve plug (20):ALS=(D52−D202)*π/4.  (I)
The effective control-side area of the prior art diaphragm assembly (Acontrol) that is exposed to control pressure is equal to the area of control diaphragm (6) minus the effective area of piston (13) where D6 is the diameter of the diaphragm (6) and D13 is the diameter of the piston:Acontrol=(D62−D132)*π/4  (II)
The effective area A20 of the prior art valve plug (20) that is exposed to downstream liquid pressure at location (19) is expressed as:A20=D202*π/4.  (III)
The force balance equation on the diaphragm assembly of the regulator valve of the prior art can be written as:(Pup*ALS)+(Pdown*A20)=(Pcontrol*Acontrol).  (IV)
In equation IV, areas ALS, A20, and Acontrol are constant. Pressure Pcontrol, the regulated setpoint pressure, is constant. The variables then are the upstream liquid pressure Pup (which one is trying to control) and the downstream liquid pressure in the lower valve body, Pdown. At steady state, both Pup and Pdown are constant, although the exact value of Pdown is unknown to the operator or an automated controller. Rearranging Eq. IV provides the equation:Pup*D52−(Pup−Pdown)*D202=(Pcontrol*Acontrol)  (V)
Consequently, a change in the controlled pressure of the upstream liquid product requires a corresponding control pressure Pcontrol that is not proportional with the change in Pup. Adjusting upstream pressure Pup requires a change in the positioning of valve member (20) to throttle up (or down) the flow of liquid through the orifice to maintain the Pup setpoint. More importantly, when an incidental change in downstream liquid pressure Pdown occurs, the total pressure differential (Pup−Pdown) across the regulator can cause a change in the liquid flow rate across the orifice. The change in liquid flow rate immediately affects the upstream pressure valve, Pup. Use of the prior art pressure regulator provides less system stability, a greater need for sophisticated control and feedback devices, and a greater variability in the upstream pressure Pup which one is trying to control at a constant value.
A process system can also employ a pressure-reducing regulator. A pressure-reducing regulator typically controls the downstream liquid pressure (a liquid pressure building regulator controls the upstream pressure). A pressure-reducing regulator of the prior art has a configuration substantially identical to that of the prior art back pressure regulator shown in FIG. 10, except that the inlet-outlet ports are reversed, and the valve member (20) is on the opposite side of the orifice 21. In general, a change in the pressure of the flow inlet (upstream liquid pressure, Pup) should not affect the downstream pressure, which is under control. However, changes in the flow inlet pressure can affect the control of the pressure in the flow outlet (the downstream pressure, Pdown) that is being controlled by the regulator. A sudden significant increase (or decrease) in inlet pressure would exert a greater (or lesser) force upon the lower face of the valve plug 20 that is transmitted to the diaphragm assembly. In the circumstance where there is no feedback control between the downstream pressure, Pdown, exiting the regulator, an increase in the force exerted against face of the valve plug 20 causes the valve plug to move toward the closed position, which in turn reduces the liquid flow through the orifice, and reduces the effective liquid product pressure, Pdown, in the outlet stream. The force balance equation for a pressure-reducing regulator is:(Pdown*ALS)+(Pup*A20)=(Pcontrol*Acontrol).  (VI)
When the areas ALS, A20, and Acontrol are constant, and the controller pressure Pcontrol is held constant, the equation V reduces to a disproportional relationship between Pdown and Pup:Pdown≈K−Pup.  (VII)
Thus, when the upstream pressure increases, the controlled downstream pressure decreases. Without a separate feedback controller, Pdown decreases below its target setpoint P′down. A feedback controller works by sensing the difference between the target setpoint pressure, P′down, and the actual downstream pressure, Pdown, and sending a corrective control signal to the control regulator. The corrective signal will increase the control pressure Pcontrol, which in turn places greater force downstream on the diaphragm assembly, and causes the flow orifice to become more open. The opening of the flow orifice increases liquid flow through the orifice and increases the downstream pressure, Pdown. The feedback controller can work well, but can take excessive time to arrive at the appropriate target liquid pressure. In some situations, frequent changes in the upstream pressure can prevent the feedback controller from reaching steady-state control of the downstream liquid pressure. Feedback control also requires additional equipment such as a pressure transmitter or transducer, and some type of control device, typically a PID controller or programmable logic controller.
Typical tactics to improve performance in conventional industrial-style pressure regulator valves are not typically suitable for use in sanitary valves For example, the pressure reducing valve of the prior art shown in U.S. Pat. No. 6,371,156 shows a typical pilot valve correction scheme used in regulating valves. The cleanability requirements of the sanitary industries can render this kind of valve render inappropriate for sanitary products since many of the valve features, such as the pilot lines 26 and 28 would be difficult to clean. Consequently, the sanitary industry has had a long-standing need for improved fluid regulating valves, and in particular for improved pneumatically-controlled pressure regulating devices, that meet sanitary standards and cleanable guidelines.